Conventionally, in radio communication systems cellular systems are used widely in which a service area of a single base station is about a few kilometers and a plurality of base stations are disposed. Further, in order to increase the number of users accommodated in a base station, the number of base stations is increased to reduce a service area per base station.
Recently, with the widespread of the internet, i mode (that is a registered trademark of NTT DoCoMo, Inc.) and so on, distribution services of image and speech information have been performed increasingly, and the data amount that a base station handles dramatically increase. The data that base stations handle includes real time data that does not permit a delay and non real time data that permits a delay. An example of the real time data is speech data, and an example of the non real time data is image data with less motion such as a background image.
However, in the conventional radio communication systems, although it is possible to increase the user capacity by reducing the service area of a base station, there is still a problem that it is difficult to greatly increase the user capacity, due to increases in control load caused by increases in data that a base station handles, in addition to increases in frequency of handover.